1 files changed, 49 insertions, 0 deletions
diff --git a/internal/resolver/hints.go b/internal/resolver/hints.go
new file mode 100644
index 0000000..c7b23b4
--- /dev/null
+++ b/internal/resolver/hints.go
@@ -0,0 +1,49 @@
+package resolver
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+type NS struct {
+	Name string
+	Addr string
+}
+
+func LoadHints(path string) ([]NS, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("hints file %s not found — download from https://www.internic.net/domain/named.root: %w", path, err)
+	}
+	defer f.Close()
+
+	var nsNames []string
+	glue := make(map[string]string)
+	sc := bufio.NewScanner(f)
+	for sc.Scan() {
+		fields := strings.Fields(sc.Text())
+		if len(fields) < 4 || fields[0] == ";" {
+			continue
+		}
+		if fields[0] == "." && fields[2] == "NS" {
+			nsNames = append(nsNames, fields[3])
+		}
+		if fields[2] == "A" {
+			glue[fields[0]] = fields[3]
+		}
+	}
+	if err := sc.Err(); err != nil {
+		return nil, err
+	}
+
+	var hints []NS
+	for _, name := range nsNames {
+		hints = append(hints, NS{Name: name, Addr: glue[name]})
+	}
+	if len(hints) == 0 {
+		return nil, fmt.Errorf("no root hints parsed from %s", path)
+	}
+	return hints, nil
+}